Alcohol and other drug use careers will be studied using data from a cohort of 2,000 individuals whose ages, through four rounds of data collection, span the life period of early adolescence to young adulthood. This study will collect a fourth round of data to add to three rounds previously collected. The fourth round will be comprised of a stratified random sample of respondents who participated in the first round (n=7,550). Substance use careers will be characterized by examining common and more serious patterns of concurrent substance use across the four rounds and the dimensions of adolescent substance use that predict patterns of use during young adulthood. This characterization will contribute to prior research by representing concurrent patterns of use at various levels (e.g., regular use, problem use) rather than simply the initiation of single substances. The study will include sufficient numbers of individuals to facilitate an in-depth study of different types of substance use careers and to focus on the careers of specific subgroups of adolescents and young adults who may be at differential risk for substance use and related problems. The study will also explore the predictors of patterns of use within careers and will compare the significant predictors for the subgroups of interest. Cases will be stratified before sampling to ensure adequate representation of these subgroups and the various patterns of substance use during adolescence. The first two of the following aims reflect the overall objective of understanding alcohol and other drug use during young adulthood and the patterns of use during adolescence and other predictors that might lead to use during this later period. The third aim addresses an important methodological issue in this type of research. The specific aims are to: 1. examine alcohol and other drug use careers from early adolescence to young adulthood for all longitudinal sample members and for subgroups of adolescents/young adults defined by sex, race, and socioeconomic, urban/rural, and high school graduate/dropout status; 2. compare predictors of alcohol and other drug use patterns for adolescents and young adults, for all sample members and within subgroups of adolescents/young adults defined by sex, race, and socioeconomic, urban/rural, and high school graduate/dropout status; and 3. examine the issue of recall of first drug use by comparing retrospective reports during young adulthood to data collected during adolescence. This study will extend knowledge about drug use patterns by including (1) age groups not typically found in one longitudinal study, (2) sufficient numbers in subgroups of interest (especially school dropouts) for comparative purposes, and (3) a large number of measures of potential and theoretically meaningful predictors of patterns.